Self-propelling unit



June 21, 1966 R. HOPPENRATH 3,256,790

SELF-PROPELLING UNIT Filed May 8, 1963 9b .9a a m 7- United StatesPatent Office 3,256,790 Patented June 21, 1966 3,256,790 SELF-PROPELLINGUNIT Rudolf Hoppenrath, Molfsee, Germany, assignor to MaschlnenfabrikBuckau R. Wolf Aktiengesellschaft, Grevenbroich, Germany Filed May 8,1963, Ser. No. 278,831

Claims priority, application Germany, May 12, 1962, M 52,835 15 Claims.(Cl. 9448) The present invention relates to self-propelling units of thetype which are equipped with one or more vibrator assemblies, and moreparticularly to an improved self-' propelling unit which is especiallysuited for use as an apparatus for tamping earth or other types ofcomminuted, pulverulent or granular material.

It is an'important object of my invention to provide a very simpleself-propelling unit which may be equipped with a conventional vibratorassembly and 'whichis capable of advancing forwardly, rearwardly, in astraight path, or in an arcuate path as long as the vibrator assemblytends to move it in parallelism with the surface of the ground.

Another object of the invention is to provide a selfpropelling unit ofthe above outlined characteristics which may be rapidly and convenientlyadjusted for movement in a selected straight or arcuate path as well asforwardly or rearwardly and which may be adjusted to vary its speed.

A further object of the invention is to provide a selfpropelling tampingapparatus wherein the assembly which causes one or more tamping elementsto compact the ground or another comminuated material simultaneouslyserves as a means for propelling the tamping elements in a selecteddirection.

An additional object of the invention is to provide an improved tampingapparatus of the just outlined characteristics which can be manufacturedin many sizes and shapes, which may be constructed and assembled in sucha way that one or more of its parts do not vibrate or are caused tovibrate to a minimal extent when the apparatus moves in a selecteddirection so that a person controlling the apparatus is not compelled toendure vibratory movements, and which can be arrested in a selectedposition if it becomes necessary to subject a selected area to a moreintensive compacting action.

With the above objects in view, one feature of my invention resides inthe provision of a self-propelling unit which comprises aground-contacting element whose underside is arranged to come to rest onthe surface of the ground (e.g., a material which must be compacted), avibrator assembly mounted on the ground-contacting element and arrangedto impart to this element reciprocatory movements in a directionparallel with the underside thereof so that the element tends to moverearwardly and forwardly along the surface of the ground, and arrestingmeans provided on the element and arranged to engage the surface of theground with a greater force when the element tends to move rearwardlyand with a smaller force (which smaller force may be zero) when theelement tends to move forwardly whereby the element is auto maticallycompelled to propel itself in forward direction as soon as the vibratorassembly is started.

The self-propelling unit of my invention may assume the form of atamping apparatus, of a toy which may be used as a vehicle on sand, onsoil or on any other type of ground, and which may also serve many otheruseful purposes wherever it is necessary to advance a load along theground at comparatively low speeds and when it is impractical to resortto wheels, rollers, caterpillar treads or similar rotary motiontransmitting parts.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved self-propelling unit itself, however, both as to itsconstruction and its method of operation, together with additionalfeatures and advantages thereof, will be best understood from thefollowing detailed description of certain specific embodiments withreference to the accompanying drawings, in which:

FIG. 1 is a schematic side elevational view of a selfpropelling unitwhich assumes the form of a tamping apparatus and which is constructedin accordance with one embodiment of my invention;

FIG. 2 is a top plan view of a ground-contacting element which formspart of a modified self-propelling unit and which is provided with aseries of transversely aligned arresting members;

FIG. 3 is a fragmentary longitudinal vertical section through a portionof a further self-propelling unit wherein an arresting member isconnected with the trailing end portion of a ground-contacting elementby means of a compressed helical spring; and

FIG. 4 is an enlarged side view of the arresting means shown in FIG. 1in operative and inoperative positions.

Referring now in greater detail to the illustrated embodiments, andfirst to FIG. 1, there is shown a self-propelling unit which assumes theform of a tamping apparatus and which serves to compact a mass ofgranular, pulverulent or similar comminuted material (e.g., earth or thelike). The apparatus comprises a plate-like tamping element 1 whoseunderside comes to rest on the surface of the material M to be tampedand which includes a centrally located major portion 1a, a leading endportion 2 whose underside is inclined upwardly and forwardly withrespect to the underside of the major portion 1a, and a trailing endportion 3 whose underside is inclined upwardly and rearwardly withrespect to the underside of the major portion 1a. The tamping element 1supports a vibrator assembly which includes a mass or weight 5, springs6 which support the mass 5 at a level above the upper side of thetamping element, a vibrator 7 of any known design, and a motor 4 whichdrives the vibrator. The vibrator assembly 4-7 is arranged to produce avertical component of force which tends to reciprocate the tampingelement 1 in a direction which is perpendicular to the underside of themajor portion 1a whereby the tamping element compacts thematerial M. Inaddition, the vibrator assembly produces horizontal components of forcewhich tend to reciprocate the tamping element in a direction which isparallel with the underside of the central portion 1a whereby thetamping element exhibits the tendency to move rearwardly and forwardlyalong the surface of the material M. In other words, rearward andforward movements are equal and alternate with each other. Of course,were the element .1 permitted to reciprocate back and forth in thismanner, the tamping apparatus would remain above a selected portion ofthe material M and would fail to tamp the entire surface or the selectedarea of such material.

In accordance with one feature of my invention, there is provided anarresting means which includes an arresting member 9 mounted at theunderside of the trailing end portion 3 and arrangedto move intoengagement with the surface of the material M and to penetrate into ofthe tamping element. The forward end of this front face is pivotallysecured to the trailing end portion 3 by means of a hinge 13 whichpermits the arresting member 9 to pivot about a horizontal axis which isperpendicular to the direction of forward movement of the tampingapparatus. The apparatus further comprises actuating means, here shownas a hydraulically or pneumatically operated cylinder and piston unit11, which operates between the underside of the trailing end port-ion 3and the arresting member 9 and which enables an operator to pivot thearresting member about the axis of the hinge 13 so that the front face9a may be moved toward or away from the surface of the material M. Inother words, the actuating means 11 enables the operator to move thefront face 9a into actual contact with the surface of the material Mwhereby the sharp edge 9b penetrates into the material when the vibratorassembly tends to move the tamping element in a direction counter tothat indicated by the arrow A.

In order that the tamping apparatus may reverse the direction of itsmovement, I prefer to provide a second arresting member 8 which ismounted belowthe underside of the leading end portion 3 and which ismirror symmetrical to the arresting member 9 with reference to a planewhich is perpendicular to the plane of FIG. 1 andwhich passestransversely across the major portion 1a of the tamping member. Thissecond arresting member comprises a face 8a which is the front facethereof when the apparatus is caused to move in a direction to the left,as'viewed in FIG. 1, and a sharp edge 8b which extends transversely ofthe element 1 and which may penetrate into the surface of the material Mwhen the arresting member is caused to pivot about the horizontal axisof the hinge 12 through the intermediary of a second arresting means 10which is secured to the leading end portion 2. Thus, if the operatordesires the tamping apparatus of FIG. 1 to propel itself in a directioncounter to that indicated by the arrow A, the actuating means 11 iscaused to move the arresting member 9 upwardly and out of contact withthe material M. In the next step, the operator causes the actuatingmeans 10 to pivot the arresting member 8 in a clockwise direction, asviewed in FIG. 1, and to move the face 8a into engagement with thesurface of the material M. The apparatus is then compelled to move tothe left because the edge 8b will penetrate into the material M wheneverthe vibrator assembly tends to move the tamping element 1 in thedirection of arrow A. The end portion 2a now becomes the trailing endportion of the tamping element.

The springs 6 enable the mass to remain at a given level when thetamping element 1 is caused to vibrate so that the mass 5 merely shareshorizontal movements of the tamping member. The operator may occupy aseat (not shown) on the mass 5 and is not compelled to endure vibrationwhen the apparatus is in use. The construction of the vibrator 7 (whichmay include suitable eccentrics or the like) is well known and by itselfforms no part of my invention. All that counts is to provide. a vibratorassembly which imparts to the tamping element reciprocatory movements ina direction at right angles to the surface of the ground and which tendsto impart to this element reciprocatory movements in a horizontaldirection (in parallelism with the surface of the ground) so that thetamping element will automatically propel itself forwardly orrearwardly, depending upon which of the two arresting members is inactual contact with the ground.

It goes without saying that the edge 8a or 9a may be replaced by aseries of teeth or the like without in any way departing from the spiritof my invention. However, the arresting members must be constructed andmounted in such a way that they offer less resistance to horizontalmovement of the tamping element in a first direction and that they offergreater resistance to horizontal movement of the tamping element in theopposite direction. Thus,

there will be some friction between the front face 9a and.

' reciprocatory movements of the tamping element so that its surface 9amay be lifted above the material M when the tamping element movesforwardly in order to eliminate friction between the surface of thematerial to be tamped and the front face 9a.

If desired, the hinges 12, 13 may be omitted and the members 8, 9 may becaused to reciprocate, rather than pivot, toward and away from theground.

FIG. 2 illustrates a portion of a modified self-propelling unit whichmay assume the form of a toy vehicle or the like and which includes aplate-like ground-contacting element 21 corresponding to the tampingplate 1 of FIG. 1 and having a centrally located major portion 21a Whoseunderside comes to rest on the ground, a transversely extending leadingend portion 22 which is bent upwardly and forwardly in the same way asthe leading end portion 2 of the plate 1, and a trailing end portion 23which is parallel with the end portion 22 and whose underside isinclined upwardly and rearwardly with reference to the underside of themajor portion 21a. In accordance with a more specific feature of myinvention, the trailing end portion 23 supports two pivotable arrestingmembers 29, 29' whose construction is identical with or analogous tothat of the arresting member 9. An important advantage of this modifiedself-propelling unit is that, by selectively moving the arresting member29 and/or 29' into contact with the surface of the ground, the operatormay steer the unit so that the latter will move in a straight path, inan arcuate path which curves upwardly (arrow 34) or in an arcuate pathwhich curves downwardly (arrow 35), depending upon whether the operatormaintains both arresting members in contact with the ground, whether thearresting member 29 is lifted upwardly and away from the ground, orwhether the arresting member 29 is moved away from the ground.Furthermore, by adjusting the extent to which the actuating means 31 or31 pivots the respective arresting member relative to the trailing endportion 23, the apparatus may be caused to move in a number ofadditional arcuate paths in response to greater or lesser frictionalengagement between the front faces of these arresting members and thesurface of the ground. Such adjustments of the arresting members willalso result in greater or lesser forward speed of the unit.

The leading end portion 22 supports two piv-otable arresting members 28,28 which are putt-o use when it is desired to propel the element-21 in adirection counter to that indicated by the arrow A. The manner in whichthe actuating means 31, 31', 30 and '30 pivot the respective arrestingmembers may be the same as described in connection with FIG. 1. Each ofsuch actuating means may assume the form of a rack and pinion or anothermechanical device. It is also possible to provide manually operableactuating means for the arresting members.

Referring finally to FIG. 3, there is shown a portion of a differentself-propelling unit which again comprises a tamping orground-contacting element 41 having a major portion 41a Whose undersidecomes into actual contact with the surface of the ground M, and atrailing end portion 43 which has an upwardly and rearwardly inclinedunderside 43a and which carries a boss 56 formed with a thorough borefor the stem of a rearwardly extending guide bolt 57. The head 57a ofthe bolt 57 abuts against the front face of the boss 56 and the rear endportion of this bolt is provided with external threads 58 which matewith a nut 59 serving to retain a wedge-' shaped arresting member 49 insuch a way that the latter I the understide 43a.

is movable in the axial direction of the bolt 57 and that its face 490may move into abutment with or away from The unit of FIG. 3 furtherincludes resilient means here shown as a compresed helical spring 60which operates between an internal shoulder 49d of the arresting member49 and one of two washers 62, 63 which are adjacent to the nut 59. Thespring 60 is ac 'commodated in a recess 64 provided in the rear face ofthe arresting member 49.

The self-propelling unit of FIG. 3 operates as follows:

The spring 60 normally maintains the face 490 in abutment with theunderside 43a and the upwardly and for- Wardly inclined front face 49aof the arresting member 49 engages the surface of the ground. When thenonillustrate-d vibrator assembly causes the element 41 to moveforwardly (arrow A), the spring 60 is compressed because the element 41moves away from the arresting member 43. This will be readily understoodsince the frictional engagement between the inclined front face 43a andthe ground is greater than the frictional engagement between theunderside of the major portion 41a and the ground. When the vibratorassembly tends to move the element 41 rearwardly, the underside 49abears against the face 490 and tends to move the member 49 rearwardlywhereby the rearward displacement of the element 41 is reduced to aminimum, particularly if the ground is comparatively hard and if thearresting member has a good grip on the ground. While the element 41moves forwardly and away from the arresting member 43, the spring 60 iscompressed and stores energy so that, at the time the underside 43a isspaced through a predetermined distance from the face 490, the springexpands as shown as it overcomes the friction between the ground and thefront face 49a whereby the arresting member 49 strikes against thetrailing end portion 43 and imparts to the element 41 an impulse whichcauses the latter to move forwardly (arrow A). In other words, thearresting member 43 may actually assist the vibrator assembly inadvancing the ground-contacting element in a given direction.

If the operator desires to reverse the direction of movement of theelement 41, the nut 59 is removed and the arresting member 49 istransferred to the leading end portion (not shown) of the element 41. Itis obvious that the unit of FIG. 3 may be equipped with two or morearresting members at each of its ends so that such unit may be steeredby moving one or more selected arresting members into contact with thesurface of the ground. Furthermore, it is equally possible to installthe arresting member or members beneath the major portion of a tampingor ground-contacting element without in any way departing from thespirit of any invention.

Referring again to FIG. 3,.the bias of the spring 60 may be selected insuch a way that this spring causes the arresting member 49 to impactagainst the trailing end portion 43 at the exact time when the element41 completes its forward stroke. In this manner, I prevent any and allrearward displacements of the element 41. Otherwise, there might be someslight rearward movement at the time the edge 49b is caused to penetrateinto the material of the ground, especially if the ground iscomparatively soft (e.g., at the outset of a tamping operation). In theunit of FIG. 3, the arresting member 49 constitutes an additional massor weight which normally tends to lag behind the ground-contactingelement and which is intermittently accelerated to strike or to impactagainst the ground-contacting element at a characteristic frequencywhich is lower than the frequency of the ground-contacting element.

If the trailing end portion of the ground-contacting element carries twoor more arresting members, the arresting members are preferably arrangedmirror symmetrically with reference to a vertical plane which intersectsthe ground-contacting element and which is parallel with the directionof forward movement of the unit.

In conventional tampering apparatus which are equipped with a vibratorassembly, it happens again and again that the apparatus comes to restbecause the rearward and forward movements caused by the vibratorassembly are of equal magnitude. This can happen when a tampingapparatus is used on slippery terrain (mud) so thatthe apparatusactually sinks into the ground if the vibrator continues to operate.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of this invention,and therefore, such adaptations should and ,are intended to becomprehended within the meaining and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by letters Patent is:

1. A self-propelling unit comprising a ground-contacting element havingan underside arranged to come to rest on the surface of the ground; avibrator assembly mounted on said element, said assembly being arrangedto at least impart to said element alternate reciprocatory movementssubstantially parallel with said underside first in one direction andthen in a direction opposite said one directionwhereby the element tendsto move alternately rearwardly and forwardly along the surface of theground; and arresting means supported by and movable with reference tosaid element between an inoperative portion in which said arrestingmeans is spaced from the surface of said ground and an operativeposition in which said arresting means engages said surface of saidground, said arresting'means having a groundengaging portion having arear edge and being inclined forwardly so as to only slidingly engagethe surface of the ground when the element together with said arrestingmeans is moving forwardly while said arresting means is in saidoperative position thereof, Whereas said rear edge bl-ockingly engagesthe surface of the ground when said element together with said arrestingmeans moves rearwardly while said arresting means is in said operativeposition thereof, whereby during said reciprocatory movement of saidelement movement of the same forwardly is made possible by said slidingengagement of said arresting means with the ground during such movement,and movement of said element rearwardly is blocked by said blockingengagement of said rear edge of said arresting means with said surfaceof the ground so that the element is compelled to propel itselfforwardly during reciprocatory movements thereof while said arrestingmeans is in said operative position.

2. A self-propelling tamping apparatus comprising a tamping elementhaving an underside arranged to come to rest on the surface of thematerial to be tamped; a vibrator assembly mounted on said tampingelement, said assembly being arranged to impart to said tamping elementreciprocatory movements in a direction substantially perpendicular tosaid underside whereby the tamping element compacts the material, and toimpart to said element alternate reciprocatory movements substantiallyparallel with said underside first in one direction and then in adirection opposite said one direction whereby the tamping element tendsto move alternately rearwardly and forwardly along the surface of thematerial to surface of the ground; and arresting means supported by andmovable with reference to said element between an inoperative portion inwhich said arresting means is spaced from the surface of said ground andan operative position in which said arresting means engages said surfaceof said ground, said arresting means having a ground engaging portionhaving a rear edge and being inclined forwardly so as to only slidinglyengage the surface of the ground when the element together with saidarresting means is moving forwardly while said arresting means is insaid operative position thereof, whereas said rear edge blockinglyengages the surface of the ground when said element together with saidarresting means moves rearwardly while said arresting means is in saidoperative position thereof, whereby during said reciprocatory movementof said element movement of the same forwardly is made possible by saidsliding engagement of said arresting means with the ground during suchmovement, and movement of said element rearwardly is blocked by saidblocking engagement of said rear edge of said arresting means with saidsurface of the ground so that the element is compelled to propel itselfforwardly during reciprocatory movements'thereof while said arrestingmeans is in said operative position.

3. In a self-propelling tamping apparatus, in combina-- tion, a tampingelement having an underside arranged to come to rest on the surface ofthe material to be tamped; a vibrator assembly mounted on said tampingelement, said assembly being arranged to impart to said tamping elementalternate reciprocatory movements substantially parallel with saidunderside first in one direction and then in a direction opposite saidone direction whereby the tamping element tends to move alternatelyrearwardly and forwardly along the surface of the material to be tamped;and arresting means supported by said tamping element at the rear endthereof and extending'rearwardly and downwardly therefrom and having arearwardly facing rear edge which slides over the surface of thematerial to be tamped when said tamping element moves forwardly andwhich tends to penetrate spaced from said tamping element into saidmaterial to be tamped when said tamping element tends to move rearwardlywhereby said tamping apparatus propels itself forwardly.

4. A self-propelling tamping apparatus comprising a tamping elementhaving an underside arranged to come to rest on the surface of thematerial to be tamped, said tamping element having a leading end portionand a trailing end portion, at least one of said end portions having abottom face which is inclined upwardly with respect to said underside ofsaid element; a vibrator assembly mounted on said tamping element, saidassembly being arranged to impart to said tamping element alternatevertical and horizontal components of force so as to cause reciprocatorymovements in a direction substantially perpendicular to said undersidewhereby the tamping element compacts the material, and reciprocatorymovements in a direction substantially parallel with said undersidewhereby the tamping element tends to move alternately rearwardly .andforwardly along the surface of the material to be tamped; and arrestingmeans supported by said tamping element at said trailing end portionthereof and extending rearwardly and downwardly therefrom and having arearwardly facing rear edge which slides over the surface of thematerial to be tamped when said tamping element moves forwardly andwhich tends to penetrate spaced from said tamping element into saidmaterial to be tamped when said tamping element tends to move rearwardlywhereby said tamping apparatus propels itself forwardly.

5. A self-propelling tamping apparatus comprising a tamping elementhaving an underside arranged to come to rest on the surface of thematerial to be tamped, said element having a leading end portion and atrailing end portion, at least one of said end portions having a bottom.face which is inclined upwardly with respect to said underside of saidelement; a vibrator assembly mounted on said tamping element, saidassembly being arranged to impart to said tamping element firstreciprocatory movements in a direction substantially perpendicular tosaid underside whereby the tamping element compacts the material, and toimpart to said element second reciprocatory movements substantiallyparallel with said underside first in one direction and then in adirection opposite said one direction whereby the tamping element tendsto move alternately rearwardly and forwardly along the surface of thematerial-to be tamped; and arresting means provided at the rear of saidtamping element and arranged to penetrate into the surface of thematerial to be tamped only when the tamping element tends to moverearwardly whereby said tamping element is compelled to propel itselfforwardly, said arresting means comprising a wedge-shaped arrestingmember having a front face which is inclined forwardly and upwardlyrelative to said underside of said tamping element so as to slide alongthe surface of the material to be tamped without penetrating thereintowhen the tamping element moves forwardly and having a rear face inclinedto said underside at an angle sharper than said front face forpenetrating the surface of the material to be tamped when said tampingelement tends to move rearwardly.

6. A self-propelling tamping apparatus comprising a tamping elementwhich includes a major portion having an underside arranged to come torest on the surface of the material to be tamped and a trailing endportion having an underside which is inclined upwardly and back: wardlywith respect to the underside of said major portion; a vibrator assemblymounted on said tamping element, said assembly being arranged to impartto said tamping element first reciprocatory movements in a directionsubstantially perpendicular to the underside of said major portionwhereby the tamping element compacts the material, and to impart to saidelement second reciprocatory movements substantially parallel with theunderside of said major portion first in one direction and then in adirection opposite said one direction whereby the tamping element tendsto move alternately rearwardly and forwardly along the surface of thematerial to be tamped; and arresting means supported by and movable withreference to said tamping element between an operative position in whichit engages the surface of the material to be tamped and an inoperativeposition in which it is spaced from said surface, said arresting meansbeing located at a level below the underside of said trailing endportion, and comprising a wedge-shaped arresting member having a frontface inclined to said underside, and a rear face inclined to saidunderside at a sharper angle than said front face and arranged topenetrate in the operative position thereof into the surface of thematerial to be tamped only when the tamping element tends to moverearwardly whereby the tamping element is compelled to propel itselfforwardly.

7. A self-propelling tamping apparatus comprising a tamping elementwhich includes a cent-rally located major portion having an undersidearranged to come to rest on the surface of the material to be tamped, afront end portion having an underside which is inclined upwardly andforwardly with respect to the underside of said major portion, and atrailing end portion having an underside which is inclined upwardly andbackwardly with respect to the underside of said major portion; avibrator assembly mounted on said tamping element and comprising arotating vibration-producing means having an axis of rotation parallelto said underside and extending transversely of the direction ofelongation of said tamping element, said assembly being arranged toimpart to said element'first reciprocatory movements in a directionsubstantially perpendicular to the underside of said major portionwhereby said tamping element compacts the material, and to impart tosaid tamping element second reciprocatory movements substantiallyparallel with the underside of said major portion first in onedirectionand then in -a direction opposite said one direction wherebythe tamping element tends to move alternately rearwardly and forwardlyalong the surface of the material to be tamped; arresting meansincluding a first and a second arresting member respectively locatedbeneath the underside of said trailing end portion and said leading endportion so as to permit reversal of direction of said apparatus, each ofsaid arresting members having a blockin-g portion arranged to penetrateinto the material to be tamped only when said apparatus moves inrearward direction; and actuating means for moving said arrestingmembers with respect to said tamping element toward and away from thesurface of the material to be tamped so that the arresting element whichis disposed beneath the underside of said trailing end port-ion may belowered into contact with the surface of the material to be tamped forpenetrating thereinto only when said element tends to move rearwardly toprevent rearward movement of said tamping element whereby the latter iscompelled to propel itself forwardly.

8. A self-propelling tamping apparatus comprising a tamping elementhaving an underside arranged to come to rest on the surface of thematerial to be tamped, said tamping element including a trailing endportion having a side inclined upwardly and rearwardly with respect tosaid underside; a vibrator assembly mounted on said tamping element,said assembly being arranged to impart to said tamping element firstreciprocatory movements in a direction substantially perpendicular tosaid underside whereby the tamping element compacts the mate-rial, andto impart to said tamping element second reciprocatory movementssubstantially parallel with said underside first in one direction andthen in a direction opposite said one direction whereby the tampingelement tends to move alternately rearwardly and forwardly along thesurface of the'material to be tamped; and arresting means including anarresting member located next to said trailing end portion and having afirst face adjacent to the side of said trailing end portion a groundengaging second face inclined to said underside, and an edge portionrearwardly spaced from said first face, said edge portion of saidarresting member penetrating into such material only when said tampingelement tends to move rearwardly whereby said element is compelled topropel itself forwardly, and resilient means arranged to bias the faceof said arresting member against the side of said trailing portion, thebias of said resilient means increasing when said tamping element movesforwardly with respectto said arresting member whereby the arrestingmember is entrained by said resilient means and its face impacts againstthe side of said trailing portion to assist the propulsion of saidtamping element.

9. An apparatus as set forth in claim 8, wherein said resilient meanscomprises at least one compressed helical spring.

10. A self-propelling unit comprising an elongated ground-contactingelement having an underside arranged to come to rest on the surface ofthe ground; a vibrator assembly located at a level above said elementand including a mass, resilient means disposed between said mass andsaid element, motor means mounted on said mass, and a vibrator driven bysaid motor and operatively connected with said element, said vibratorincluding a rotating eccentric having an axis parallel to said undersideand extending transversely of the direction of elongation of saidelement being arranged to at least impart to said element reoiprocatorymovements substantially parallel with said underside first in onedirection and then in a direction opposite said one direction wherebythe element tends to move rearwardly and forwardly along the surface ofthe ground; arresting means provided on said element and adapted toslidingly engage the surface of the ground when said element tends tomove forwardly and to blockingly engage the surface of the ground whenthe element tends to move rearwardly whereby the element is compelled topropel itself forwardly, said arresting means comprising a face inclinedto said underside in forward direction so as to slide over said surfaceduring forward movement, and a trailing edge as said face whichblockingly engages said surface during rearward movement of saidelement; and selective means for selectively placing said arrestingmeans into engagement with the ground.

transversely of the direction of forward movement of said element, eachof said arresting members being provided with an inclined face and arear edge, and wherein saidselective means comprises actuating means forselectively moving said elements into and away from contact with theground so that the unit may be steered to advance in a desired path inresponse to movement of the respective rear edges of selected arrestingmembers into blocking contact with the ground.

12. A self-propelling tamping apparatus comprising a tamping elementhaving an underside arranged to come to rest on the surface of thematerial to be tamped and having a front edge and a rear edge havingrespective bottom faces upwardly inclined relative to said underside; avibrator assembly mounted on said tamping element and including arotating eccentric having an axis of rotation parallel to said undersideand extending transversely of the direction of elongation of saidelement, said assembly being arranged to impart to said tamping elementalternate vertical and horizontal components of force whereby thematerial to be tamped is compacted and said element tends to moveforwardly and rearwardly along the surface of said material; arrestingmeans supported by said element and including wedge means movablymounted on said front and rear edges of said element; said wedge meanshaving one face inclined upwardly and forwardly relative to said surfaceand having at its trailing end another face inclined upwardly relativeto said surface at a greater angle than said one face and adapted toblockingly engage the surface of said material to be tamped when saidelement tends to move rearwardly; and means for selectively raising andlowering said edge portion of said wedge means into blocking engagementwith the surface of the material to be tamped when the tamping elementtends to move rearwardly whereby said element is compelled to propelitself forwardly.

13. A self-propelling tamping apparatus comprising a tamping elementhaving an underside arranged to come to rest on the surface of thematerial to be tamped and having a front edge and a rear edge havingrespective bottom faces upwardly inclined relative to said underside; avibrator assembly mounted on said tamping element and including arotating eccentric having an axis of rotation parallel to said undersideand extending transversely of the direction of elongation of saidelement, said assembly being arranged to impart to said tamping elementalternate vertical and horizontal components of force whereby thematerial to be tamped is compacted and said element tends to moveforwardly and rearwardly along the surface of said material; arrestingmeans supported by said element and including wedge means movablymounted on said front and rear edges of said element, said wedge meanshaving a first surface upwardly inclined relative to said underside andhaving an edge portion adapted to blockingly engage the surface of saidmaterial to be tamped when said element tends to move rearwardly, saidwedge means further having a second surface upwardly inclined relativeto said underside of the element at a lesser angle than said firstsurface when said edge portion of the wedge means is in engagement withthe material to be tamped; and means for selectively raising andlowering said edge portion of said wedge means into blocking engagementwith the surface of the material to be tamped when the tamping elementtends to move rearwardly so that said lower surface of said wedge meansoffers less resistance to forward motion of said element than theblocking engagement of said edge portion with the surface of thematerial to be tamped offers to rest on the surface of the material tobe tamped and having a front edge and a rear edge having respectivebottom faces upwardly inclined relative to said underside; a vibratorassembly mounted on said tamping element and including a rotatingeccentric having an axis of rotation parallel to said underside andextending transversely of the direction of elongation of said element,said assembly being arranged to impart to said tamping element alternatevertical and horizontal components of force whereby the material to betamped is compacted and said element tends to move forwardly andrearwardly along the surface of said material; arresting means supportedby said element and including a ground-engaging portion adapted toblockingly engage the surface of said material to be tamped only whensaid element tends to move rearwardly; and means for selectively raisingand lowering said ground-engaging portion of said arresting means intoblocking engagement with the surface of the material to be tamped whenthe tamping element tends to move rearwardly, said ground-engagingportion having a first surface upwardly inclined relative to saidunderside and defining an edge portion, and a second surface upwardlyand forwardly inclined to said underside at a lesser angle than saidfirst surface, said ground-engaging portion being arranged to offer lessresistance to forward rnovement of said element than to rearwardmovement thereof during which latter it blockingly engages the surfaceof the material to be tamped, whereby said element is compelled topropel itself forwardly.

15. An apparatus as set forth in claim 14, wherein said arresting meansincludes a plurality of arresting members each having a ground-engagingportion, each References Cited by the Examiner UNITED STATES PATENTS1,955,101 4/1934 Sloan 9448 2,223,024 11/ 1940 Beierlein 9448 2,224,50612/ 1940 Baily 9448 2,737,094 3/1956 Jackson 9448 2,771,012 11/1956Jackson 9448 JACOB L. NACKENOFF, Primwry Examiner.

1. A SELF-PROPELLING UNIT COMPRISING A GROUND-CONTACTING ELEMENT HAVINGAN UNDERSIDE ARRANGED TO COME TO REST ON THE SURFACE OF THE GROUND; AVIBRATOR ASSEMBLY MOUNTED ON SAID ELEMENT, SAID ASSEMBLY BEING ARRANGEDTO AT LEAST IMPART ON SAID ELEMENT ALTERNATE RECIRPROCATORY MOVEMENTSSUBSTANTIALLY PARALLEL WITH SAID UNDERSIDE FIRST IN ONE DIRECTION ANDTHEN IN A DIRECTION OPPOSITE SAID ONE DIRECTION WHEREBY THE ELEMENTTENDS TO MOVE ALTERNATELY REARWARDLY AND FORWARDLY ALONG THE SURFACE OFTHE GROUND; AND ARRESTING MEANS SUPPORTED BY AND MOVABLE WITH REFERENCETO SAID ELEMENT BETWEEN AN INOPERATIVE PORTION IN WHICH SAID ARRESTINGMEANS IS SPACED FROM THE SURFACE OF SAID GROUND AND AN OPERATIVEPOSITION IN WHICH SAID ARRESTING MEANS ENGAGES SAID SURFACE OF SAIDGROUND, SAID ARRESTING MEANS HAVING A GROUNDENGAGING PORTION HAVING AREAR EDGE AND BEING INCLINED FORWARDLY SO AS TO ONLY SLIDINGLY ENGAGETHE SURFACE OF THE GROUND WHEN THE ELEMENT TOGETHER WITH SAID ARRESTINGMEANS IS MOVING FORWARDLY WHILE SAID ARRESTING MEANS IS IN SAIDOPERATIVE POSITION THEREOF, WHEREAS SAID REAR EDGE BLOCKINGLY ENGAGESTHE SURFACE OF THE GROUND WHEN SAID ELEMENT TOGETHER WITH SAID ARRESTINGMEANS MOVES REARWARDLY WHILE SAID ARRESTING MEANS IS IN SAID OPERATIVEPOSITION THEREOF, WHEREBY DURING SAID RECIPROCATORY MOVEMENT OF SAIDELEMENT MOVEMENT OF THE SAME FORWARDLY IS MADE POSSIBLE BY SAID SLIDINGENGAGEMENT OF SAID ARRESTING MEANS WITH THE GROUND DURING SUCH MOVEMENT,AND MOVEMENT OF SAID ELEMENT REARWARDLY IS BLOCKED BY SAID BLOCKING OFSAID ELEMENT REARWARDLY IS OF SAID ARRESTING MEANS WITH SAID SURFACE OFTHE GROUND SO THAT THE ELEMENT IS COMPELLED TO PROPEL ITSELF FORWARDLYDURING RECIPROCATORY MOVEMENTS THEREOF WHILE SAID ARRESTING MEANS IS INSAID OPERATIVE POSITION.